<!DOCTYPE html>
<html>
<head>
<style>
  .a { visibility: visible; }
  .b { visibility: collapse; }
  body.flip .a { visibility: collapse; }
  body.flip .b { visibility: visible; }
</style>
</head>
<body>
<div role="toolbar">
  <div role="heading" aria-label="Heading" class="a"></div>
  <div role="banner" aria-label="Banner" class="b"></div>
</div>
<script>
  function go() {
    document.body.className = 'flip';
  }
</script>
</body>
</html>
